毛竹扩张对杉木林土壤微生物残体碳积累的影响

Effects of Moso bamboo expansion on accumulation of soil microbial residual carbon in Chinese fir forest

亚热带毛竹扩张对杉木林土壤微生物残体碳积累的影响及机制尚不清楚。以毛竹向杉木林扩张带(包括杉木林、杉木-毛竹混交林和毛竹林)的凋落物(O层)和不同发生层土壤(A层、B层和BC层)为研究对象,通过分析凋落物和土壤样品中的氨基糖含量来表征微生物残体碳累积效应,并进一步评价微生物在土壤有机碳(SOC)形成过程中的作用。结果表明:毛竹扩张使杉木林凋落物数量和碳含量显著降低,但是凋落物中真菌残体碳(MRC-f)、细菌残体碳(MRC-b)和微生物残体碳(MRC)含量均显著增加;毛竹扩张显著提高了杉木林SOC、MRC-f、MRC-b和MRC含量,而且在毛竹扩张初期(杉木林演替为杉木-毛竹混交林)MRC-f、MRC-b和MRC在SOC中的比例也显著增加,说明毛竹扩张增强杉木林土壤MRC累积效应的同时,也提高了微生物对有机碳的贡献。而毛竹扩张后期MRC-f、MRC-b和MRC占SOC比例并没有显著变化,意味着毛竹扩张后期MRC和植物源残体碳对SOC含量的提升均有贡献,且两者贡献的相对比例保持不变。土壤MRC含量随着剖面深度的加深逐渐下降,而MRC占SOC比值却随着土壤深度的增加而逐渐升高,说明深层土壤中微生物对有机碳贡献高于表层土壤。研究结果对于理解微生物在亚热带森林SOC形成过程中的作用,科学评估毛竹扩张对亚热带森林生态系统及气候变化的影响,并采取合理的营林措施提升亚热带森林土壤碳汇功能具有重要理论意义。

The effects of subtropical Moso bamboo expansion on carbon accumulation in soil microbial residues in Chinese fir forests and its mechanisms were not clear. In this study, the litter(O layer) and soils of different pedogenic horizons(A horizon, B horizon, BC horizon) in the expansion zone of Moso bamboo to Chinese fir forest(including Chinese fir forest, Chinese fir and Moso bamboo mixed forest, and Moso bamboo forest) were studied. We analyzed the amino sugar content in litter and soil samples to characterize accumulation of the microbial residual carbon and further evaluated the role of microorganisms in soil organic carbon(SOC) formation. The results showed that Moso bamboo expansion significantly reduced the amount and carbon content of litter in Chinese fir forests, but significantly increased the content of fungal residual carbon(MRC-f), bacterial residual carbon(MRC-b), and total microbial residual carbon(MRC). Moso bamboo expansion significantly increased SOC, MRC-f and MRC-b and MRC in Chinese fir forests, and the proportion of MRC-f and MRC-b and MRC in SOC increased significantly at the beginning of Moso bamboo expansion(when Chinese fir forests evolved into Chinese fir and Moso bamboo mixed forest). These results indicate that Moso bamboo expansion enhanced the cumulative effect of soil MRC in Chinese fir forests and also increased the microbial contribution to SOC. However, in the late stage of Moso bamboo expansion, the proportion of MRC-f, MRC-b, and MRC to SOC did not change significantly, implying that the contribution of MRC and plant-derived carbon to the SOC content increased at the later stage of Moso bamboo expansion, and the relative proportion of their contribution remained unchanged. The content of MRC gradually decreased with soil depth, while the proportion of MRC to SOC gradually increased with the depth of the soil, implying that the microbial contribution to SOC was higher in deep soils than in surface soils. The results of the study have important theoretical implications for understanding the role of microorganisms in SOC formation in subtropical forests, scientifically assessing the impact of Moso bamboo expansion on the subtropical forest ecosystems and climate change, and adopting reasonable forestry measures to enhance the soil carbon sink function in subtropical forests.